1. Field of Invention
The present invention relates to an alignment method for assembling substrates without fiducial mark and more particularly to an alignment method for assembling substrates which employs characters of surface shapes of substrates as referenced fiducial marks to calculate movement compensation values of the substrates without other fiducial mark.
2. Related Art
In the technological fields of liquid crystal display, semi-conductor chip and printed circuit board (PCB), precise stacking and alignment for the assembling of a plurality of substrates are demanded, so that various alignment apparatuses and special fiducial marks are developed by manufacturers in order to align and assemble substrates more precisely and speedily.
Refer to FIG. 1 for an example, the Taiwanese Patent No. 1288365 applied by the applicant of the present invention discloses an alignment fiducial marks design for an alignment and movement control system of dual plates and its image processing method, an existing alignment and movement control method of dual plates is provided for precise alignment of a first plate and a second plate, it mainly includes following steps of:
In a step (S1): providing two sets of alignment fiducial marks 111 and 121 disposed at same positions on two opposite sides on a first plate 11 and a second plate 12, respectively;
In a step (S2): obtaining two sets of composite images of the alignment fiducial marks 111 and 121 by two image capturing devices 13 disposed at two opposite sides of the first plate 11 or the second plate 12;
In a step (S3): calculating offset values of two sets of coordinates of the composite images by an image processing method to obtain the offset values (ΔX1, ΔY1), (ΔX2, ΔY2) of the two coordinate sets;
In a step (S4): obtaining offset values ΔX1, ΔY1 of positions and an offset value Δθ of angle between the first plate 11 and the second plate 12 by calculating the offset values of the two coordinate sets; and
In a step (S5): compensating the offset values of positions and the offset value of angle by a tri-axial movement control module 14.
The alignment and movement control method of dual plates employs the circular alignment holes as well as cross, circular or rectangular alignment fiducial marks as the alignment fiducial marks 111 and 121 between the first plate 11 and the second plate 12. Even though the precise alignment of the dual plates can be done automatically and speedily, the alignment process may not be able to be finished smoothly because of the overlapping of images; and the alignment holes and alignment fiducial marks have to be pre-designed on the two substrates separately, which will increase the work procedures and costs.
Therefore, an improved alignment method for assembling substrates is required to solve the existing problems of the conventional techniques.